For a significant part of the year, large areas in North America have temperatures that fall well below freezing at night (10 or 20 degrees) but are well above freezing during the day. This common situation greatly limits the use of the great majority of Recreational Vehicles (RVs) with on-board water systems such as motor homes, camper trailers, travel trailers, truck slide-ins and other mobile recreational living structures and units. When the outside temperature drops below freezing, the water system must be drained to prevent damage to the pipes, tanks, water fixture(s) and other plumbing components. Very few options are available to avoid this damage. The three basic options are a) drain the water system and go without running water, b) go south to a warmer climate, or c) put the unit in storage.
Some Recreational Vehicles are equipped with dedicated heating devices such as an electric holding tank heaters and pipe heaters. These electric heating devices use 120V AC or 12V DC power. Operating these heating devices on 120V AC requires an external power source or running an on-board generator that consumes the limited on-board fuel supply. Running the heaters on 12V DC puts a significant load on the on-board battery system that is also required to operate essential on-board equipment and devices. Some larger units employ a multiple battery system that will handle heavier electrical demands but this is costly, requires more space, more weight, more maintenance, and only increases operating time by a relatively small factor. This type of low temperature protection is generally limited to larger class “A” motor homes that are equipped with high generator capacity and much larger holding tanks than are found in most RV units.
Some Recreational Vehicles locate holding tanks and run all water supply lines inside the warmed interior. This method reduces valuable interior space. One manufacturer uses a brute force approach by ducting part of the hot air output from the on-board furnace to an enclosed holding tank area and water supply line routing areas. This furnace duct method, according to the manufacturer, can provide freeze protection down to −30° F. For this extreme low temperature protection the manufacturer uses a much higher capacity furnace, thicker walls to accommodate additional insulation to provide a higher “R” value then would be needed for less extreme temperature conditions and that again reduces interior space. Another major disadvantage for this method is higher consumption of the limited on-board fuel and electrical supply. The manufacturer suggests that the unit be connected to external LP gas cylinders and connected to external 120V AC when the unit is unoccupied for any extended period of time between outings.
Winterizing the water system when traveling because the outside temperature drops below freezing is troublesome, time consuming and a costly chore. This same onerous situation can arise when parking or storing the unit for a few days or weeks between outings. The few Recreational Vehicle units that offer any real low temperature protection are notably more expensive and really not practical for most Recreational Vehicle owners. Unless the Recreational Vehicle is at a location where there is external electrical power the Recreational Vehicle must continuously run an electrical generator consuming limited on-board fuel supplies. This is a major problem for buyers who must consider the investment verses real use and limited use or opt in favor of other less troublesome and less limiting options.
For the few people who would even consider using the Recreational Vehicle for ice-fishing, hunting or exploring especially when the temperature is −30° F. below or even 0° F. outside there is a manufacturer who can cater to their extreme demands. There seems to be no practical solution or cost effective options available to the vast majority of Recreational Vehicle owners that would allow them to use and enjoy their units to the fullest by extending the recreational season, not by just a few days or weeks but months. Because the temperatures may drop below freezing for a few hours or even a few days restricts Recreational Vehicle owners to where and when they go.
As many people put it: “you can stay hundreds of days in very nice hotels or cabins with all the comforts and amenities for the cost of most RV units without being so limited as to when you go or where you go.” Some people say, “just go south when it gets cold”. That may be an option for retired people but most people who own units or would buy a nice Recreational unit, work and have families and can not go south. For the better part of the year these units have to be winterized, parked and sit until summer approaches. Even many class “B” and “C” motor homes are relegated to less than a convenient passenger vehicle which for a very few people may help them justify a more expensive motorhome over the purchase of less costly trailers, fifth-wheels or slide-ins. Many retired people purchasing a modest Class “A” motor home, a large trailer or large fifth wheel, want a unit with lots of room because as they go south for six month of the year. Although many of these people envy the freedom and mobility offered by smaller recreational trailers, fifth-wheels, slide-ins and smaller motorhomes they are still faced with going south for the better part of the year because of the low temperature limitations. Many people settle for less then they want, less then they can afford and less then they deserve because of cold weather.
Besides having to be cost effective for both the manufacturer and customer, the system must extend the full usefulness of the units' water supply system to a more functional and reasonable low temperature range. To design a RV water freeze protection system that is practical, cost effective and extends the RV season by months the on-board water warming and circulating system included the following criteria:
A) Reasonable low temperature protection should prevent freezing in static air temperatures down in the single digits range and down into the 10 to 20° F. range when moving at highway speeds of 55 to 75 MPH with wind chill affects.
B) Utilization of existing on-board equipment such as the water heater, water pump and water system supply lines.
C) Efficiency and effectiveness of the system is a critical design factor because of limited on-board electrical and fuel supplies.
D) As many parks have quiet time from 11 PM to 7 AM the system should be able to operate independently for a minimum of 8 hours, utilizing only the on-board battery and LP gas while providing freeze protection down to at least 20° F. outside air temperature without requiring running a generator or the need to be connected to any external electrical power or gas source.E) Using the existing water pump to provide pressure for the water warming circulating lines.F) Using the existing gas/electric water heater will provide the source of hot water for warming the water holding tank and also provide warming of the water supply system lines.G) Many manufacturers use custom shaped fresh water holding tanks that are expensive therefore any method of warming the tank water and monitoring the water temperature should be accomplished with little or no modification.H) The fresh water holding tanks water temperature should be monitored by a thermostat located in the tank or if applicable attached through or to the outside of the tank. When the tanks water temperature drops below the set point, the thermostat will close and power a solenoid valve that opens the hot water circulating line which empties into the holding tank and warms the holding tank water. The thermostat low temperature close point (as an example) set at 45° F. with an open differential of 5° F. minimum to reduce system cycling.I) Protecting the water supply lines includes the pump and the pumps intake water line that runs to the fresh water holding tank.J) The circulating warming and water supply lines should be bundled, wrapped in a plastic guard or shroud and then insulated to provide efficient thermal convection warming.K) The bundled water line routing should be able to follow existing water line routing without major routing changes. Many manufacturers connect the water fixtures by tapping off the main hot and cold water header/supply lines that in most plumbing configurations do run outside of the insulated warmed interior or do not run close to water fixtures. The warming system requires that any water lines running outside between water fixtures or devices should be looped inside the warmed interior then routed back outside while maintaining a bundled configuration.L) Heat loss will differ between the fresh water holding tank and the bundled water supply lines therefore a second water circulating warming loop controlled by a separate solenoid valve and thermostat is required when only the water lines need warming. Using the warm holding tank water to warm the water lines will prevent over heating of the holding tank water and reduce water heater cycling and fuel consumption that would result if only the hot water tank warming line was used.M) Preventing water fixtures from freezing inside the unit requires a furnace with the thermostat set appropriately.N) The system should be able to operate without using any on-board fuel or battery power when the unit is plugged into an external electrical power source. This is accomplished by equipping the unit with a gas/electric water heater and power converter/charger that automatically senses and switches to external electrical power when the unit is plugged into an external power source. This would also require using a small 120V AC electrical space heater inside the unit to warm the interior instead of the LP gas furnace when plugged into external electric power source in moderate freezing outside temperature. This would reduce the need to run the LP gas furnace except for very cold temperatures.O) Simple customer control of system.P) Emphasis on cost of material and parts.Q) Emphasis on installation labor cost.R) Minimum modification to existing water system line routing.S) Benefits to customers, sales and marketing.